Sound reproducer



Oct. 24, 1933.

E. H. SMYTHE SOUND REPRODUCER Original Filed Aug. 17, 1926 Patented Oct. 24, 1933 PATENT OFFICE SOUND REPRODUCER Edwin H. Smythe, Evanston, Ill., assignor, by mesne assignments, to Western Electric Company, Incorporated, New York, N. Y., a

ration of New York Original application August 17, 1926, Serial No. 129,731. Divided and this application January 4, 1929. Serial No. 330,172

18 Claims.

This invention relates to sound reproducers adapted to act directly on the air and to impart vibrations to the air from relatively large surfaces.

This is a division of my application, Serial No. 129,731, filed August 17, 1926, issued as Patent 1,895,494 on January 31, 1933.

An object of the invention is to reproduce efilciently and faithfully all sounds within the audible range.

A related object of the invention is to distribute sound vibrations uniformly over one or more sound radiatingsurfaces.

Another object of the invention is to transmit sound waves in phase from a plurality of direct acting sound radiating surfaces.

In one of its embodiments the invention provides one or more large radiating surfaces driven substantially edgewise with respect to the general plane of the surfaces, the compressional and extensional stresses in the material produced by the driving force being converted into movements of the surface transverse to its plane, these movements setting up sound waves in the surrounding air. Such a structure is relatively rigid in the direction of drive and yielding in a direction transverse thereto.-

The invention in another of its embodiments provides a sound radiator in the form of a hollow structure havingside walls of light elastic material which are driven toward and away from each other in response to a driving force common thereto. The driving force is applied to the radiator in such a way that the sound vibrations involve relatively large areas and are distributed substantially uniformly over the side walls. In a particular embodiment of the invention the radiator comprises a tubular member having two side walls which are supported at a point intermediate the ends of the walls and are driven in unison at an end of the walls ina direction substantially edgewise or perpendicular'to the plane of the support.

In a modified form of theinvention each side wall of the radiator is composed of two flat transversely rigid sections joined together to form an extended surfaceand driven at the point of junction of the two sections. Each side wall maybe made transversely rigid'by ribs or corrugations, the driving force being applied at the middle of the wall, while the opposite ends of the wall are so mounted as to be constrained against transverse movement.

In one embodiment of the invention the side Walls of the radiator are bulged in opposite directions sothat the movement of the driven, edge toward and away from the support in response to the vibration of the driving member produces a transverse movement of the walls in opposite di-, rections. The walls of the radiator may be alike in area, mass and rigidity, and when actuated by the common driving unit are caused to transmit waves that for the low frequencies are in substantially the same phase over the exterior surfaces and are in the opposite phase over the interior surfaces of the radiator, the resulting air Waves of opposite phase being separated from each other by the walls of the radiator to avoid neutralization of their effects. This construction tends to increase the effective sound radiation of the device.

In constructing the radiator in accordance with the invention there are a number of factors which may be varied to produce any desired action with respect to frequency response. The walls of the radiator may be made of various materials, of various dimensions, and of various curved and angular relations between the parts, and the weight and stiffness of the walls may be varied to give the radiator the required mass and elasticity constants for transmitting, converting into required relative movements, and distributing the driving 'force. A simple and efiicient driving member, preferably in the form of a long, light and rigid tube, as disclosed and described in the parent application heretofore referred to, may also be provided for applying the driving force uniformly along the extended edge or intermediate portion of the radiator.

The various features of the invention will be described in connection with the accompanying drawing in which like reference characters designate similar parts in the several figures, and in which:

Fig. 1 is a perspective view of a sound radiator having curved walls with a support intermediate the ends of the walls;

Fig. 2 is a perspective view of a sound radiator having side walls formed of two rigid flat sections;

Figs. 3, 3A, and 4 illustrate three modifications of the sound radiator shown in Fig. 2 including modified driving and supporting means. In Fig. 3A the driving means is shown connected to the diaphragm slightly off center in order to clarify the showing. v

The sound radiator shown in Fig. 1 comprises a long, hollow structure having two enclosingside walls 5 and 6 of light, elastic material, such for example as stiff paper, fastened together along their upper longitudinal edges preferably by means of a rigid binding strip or a rib 7 of light material such as duralumin.

The diaphragm comprising the walls 5 and 6 may be mounted on a base 9 between a pair of tubular uprights 10 and may have a driving element connected to the member 16 as shown and described in the aforementioned parent application.

The support for the diaphragm 5, 6 comprises a bowed bridging member '73 mounted on an angular supporting bar '74 which extends longitudinally through the diaphragm, the bar 74 being in turn mounted on the base 9. Opposite upturned edges of the bridging member 73 are fastened, for example, by means of cement to the inner surfaces of the diaphragm walls 5 and 6.

The motor element 12 for actuating the walls 5 and 6 is carried by support 13 mounted on vertical rods 14, which are supported in the tubular uprights 10 secured to the base 9. The rods 14 may be locked in any desired vertical position by means of suitable screws 15. The motor element 12 may be of the type disclosed and claimed in U. 8. Patent 1,709,571, issued April 16, 1929 to H. C. Harrison. The driving rod of the motor element is connected to the longitudinal rib '7 of the radiator by means of the clamping member 16 mounted midway between the ends of the radiator. Since walls 5 and 6 of the radiator are curved outwardly from each other a downward movement of the driven edge '7 will drive the walls of the radiator away from each other and increase the volume of the space enclosed between them. With a pair of walls 5 and 6 having similar mass and elasticity constants, the device when actuated by low frequency vibrations will act upon the air as a pulsator sending out from the two outer walls air pressure waves of corresponding phase and amplitude, the corresponding waves of opposite phase produced by the inner surfaces of the walls being prevented from direct intermingling with the waves from the outer surfaces by the interposition of the material of the elongated walls of the radiator.

The degree of. curvature of the radiating surfaces 5 and 6 may be varied by adjusting the angle at the joining of the edges of the two walls. Generally, the slighter the normal curvature of these surfaces with respect to the direction of application of the driving force, the greater will be the volume change in the enclosed space between the two surfaces for a given movement of the driving element. As the curvature of the surfaces approaches the semi-circular, the volume change becomes less, and beyond this point the volume change for the same direction and amplitade of movement at the driving point is in the opposite direction. Furthermore, the less the curvature the greater is the rigidity of the structurn-in the direction of drive, and correspondingly the greater is the length of wave in the material and the greater is the area involved. Accordthe normal curvature of the walls 5 and 6 should be less than semi-circular and preferably of relatively slight curvature. The walls 5 and 6 should also be secured at their driven edge in such a. way that the curvature of all points between these edgesis in the same direction, as illustrated. This is necessary since any double curvature or buckling of the walls would tend to produce transverse movement of the same surface in opposite directions and thus reduce the amount of radius of the transmitted waves.

Gne advantage secured by the above structure is that which arises from the air transformer effect at low frequencies between the inner surface of the doublewalied diaphragm and the openings at the ends thereof. Under proper conditions, the relation of the inner surface area to the area of the openings at the ends of the hollow structure will be such as to add air mass reactance to the diaphragm throughout the lower frequency range, and thus permit a relatively stiff diaphragm structure to be employed without loss of the low frequency tones. The transformer ratio may be changed as desired by changing the length or shape of the hollow structure, or both, in order to obtain the required ratio between the area of the active inner surfaces and the area of the opening of the enclosed space into the outer air. Another advantage of this structure lies in the baffle-plate action of the structure in that the portions of the M3115 more remote from the driving point function as separating walls between tbe areas of compression and rarefaction on the outer and inner surfaces of the diaphragm.

If desired, the bridging member 73 may be made of a sheet of light, stiif material similar to that of the walls of the diaphragm, in which case the transverse component of the movement due to the driving force will cause sound radiation directly from the surfaces of the bridging member, while the longitudinal component of movement that moves the walls 5 and 6 in opposite phase to produce a pulsator action will cause sound radiation from the surfaces of these walls. The bridging member 73, however, in this particular embodiment, need not be a radiator of sound energy, but may serve nerely to cooperate with the driving edge in causing the transverse movement of the balanced walls of the diaphragm. In the performance of this function it may be replaced by open arms or toggle lever connections between the supporting bar '74 and the side walls. By attaching the supporting member along the middle of the side walls, the lower half of the tubular member is left free to execute movements symmetrically with those of the upper half in response to the vibrations applied to the upper driving edge.

Fig. 2 illustrates a modification of the invention on which the side walls of the diaphragm instead of being curved, are each composed of two fiat, transversely rigid sections. The side walls 76 and 77 may each be constructed in two substantially rectangular sections, and each section may comprise two sheets of material such as light, stiff paper. One of the sheets of material of each section of a wall is preferably ridged or corrugated at intervals, the corrugations being more or less closely spaced, while the other sheet of material is flat and is pasted or cemented to the corrugated sheet. The portions of the corrugated sheet lying between adjoining corrugations are in a fiat plane, thus producing a composite wall with one flat surface and one corrugated surface with the corrugations spaced at any desired interval, and the wall being light and having a very satisfactory degree of transverse rigidity. The borders of the flat sheet of each wall section may project beyond the borders of the corrugated sheet at each edge, the adjoining edges of the fiat sheets being fastened together in any suitable manner, as by means of cement, to provide hinged connections '78 between adjoining transversely rigid sections. The lower edges of the walls '76 and 77 are fastened together in any suitable manner, and may be supported in a slotted base '19. The upper edges of the diaphragm walls are fastened together by means of a longitudinal 'ber of the for rib which is adapted to be drivenin a direction perpendicular to the plane of the support '79 in a manner similar to that described in connection with l, or the j'nction edge may be driven by the power distributing tube or torsional line drive element as described and shown in the parent application.- 1

Fig, illustrates a composite systern of sound radiating g element" of a numven'tion hereinbeiore described. In ti constructi walls of system are preferably of the i rrn illustrated Fig. 2, transvers 'gid by ridges or corrugations. The ide walls 75 7! are made up or" four rectang ar transvers iv 1 id sections secured together at thei adjoining edges. Bridging diametrica opposite junction points or edges of side we. c '76 and '77 is a radiating sur-. face consi. ting of transversely ri id sections 82 joined together and driven at an intermediate point by ti": motor el"' ent 86. This motor element as supporting bar 83, which i oi the structure ca..-ies an l... ension es through the medium oi which the whole radiating system of the diaphragm is the lower junction line of ound. movement which is imparted to the transverse radiating face by the motor element 85 causes the transverse portion 32 to act as a sound radiator, and iinp rt .nsverse lo enient to the side and 77, 1210 nt also resulting in radiation. of sound waves from the side walls. It may be seen that the sound. radiator of Fig. 3 represents the conhination of a number oi Sim-- pler elements which have a capacity of operating independently of other of the combination as sound For ins 166. the upper halves oi the walls '76 l? e noved from the combination, the part which is left, ing of the lower half of each of the side nod to the outer edges of the transverse member 82 constitute an operative cause it to radi :o to produce a coinpon- .-.l verse to the dirrtion of drive that cause, the i316" oi the ls. side wall members and rauia 'og of soup i llOZll them. Gr if lo er side woul portions 16' and 77 in the simplified co nent of the structure of Fig. 3 just considered, are deprived of their sound radiating capacity rei n merely their capacity for affording suppo for the outer edges of a transverse radia which constrain the outer edges ansverse ovement or movement i1. irecuon of the d force, the transvers ember then. the sole The system of Fig. 3,

L of a number c;

indepen ently of cornl combine their ran-.ating ing force may be applied at the transverse ineinber elongated power the pai t applica heretofore ntioned.

The sound radiator own in Fig. i is generally similar to the structure shown in Fig. 1

line of the cans of with respect to the point of application of the drivingforce and the means for supporting the mov-. ing system, and resembles the structure shown in Fig. 3 in matter of the nature of the radia straint in the direction of the driving force and the iieedoin transverse to the direction of the driving force afforded by the bridging member 82 cause the lower sections of the diaphragm walls to execute a niovernentfor low frequencies symmetrical with the movements of the upper sections or" the walls. The transverse component of movement of the side walls is accentuated by disposing the elements 82 of the bridging member at a more acute with respect to each other. Various structural modifications may be made in e sound radiator as described above without dopai from the scope and spirit of the invention. In all or" the modifications illustrated, for (EX-T211316, the hollow diaphragnis be so mounted the line of support and the line of drive are vertical instead of horizontal. In some cases where very large diaphragms are employed, a vertical support and a vertical drive may have the advantage of preventing any biasing of the driving armature that might result from the weight of the diaphragm parts that are to be moved.

What is claimed is: v r

1. A sound reprouucer comprising a hollow structure with yielding walls, a bridging member within said structure connecting said walls and hinged thereto, and means for producing relative movement in response to sound vibrations between said bridging member and said walls.

2; A sound reproducer comprising a hollow open-ended structure having a pair of yielding Walls bowed in opposite directions, a bridging member within said structure hinged to said walls at the mid portions thereof, and means for driving said member in response to sound vibrations.

3. A sound reproducer comprising a partial enclosure with yielding walls, a bridging partition within said enclosure joined to said walls, said bridging partition being normally bowed, and means for producing relative movement between apoint on said partition and the walls of said enclosure in a direction to change the shape of said partition, said movement being in accordance with vibrations representing sound.

4. A sound reproducer comprising a support, a hollow, open-ended direct-acting sound radiating surface hinged at an edge to said support, and

means for driving said surface at a point remote from said hinged edge.

5. A sound reprcducer comprising a hollow structure with yielding walls, a support, a bridging member mounted on said support and hinged double-wall diaphragms joined together edge to edge, means for supporting said diaphragms, and

ileans for driving said diaphragms at their junc- 8. A sound reproducer comprising a hollow structure having a plurality of oppositely disposed spaced sound radiating surfaces, a bridging member within said structure having its edges adjacunt those of said sound radiating surfaces, a support for said surfaces, and driving means mounted on said support and attached to said bridging member intermediate its ends, whereby actuation at said bridging member in accordance with sounds to be reproduced causes relative movement of said surfaces and said member thereby produoing acoustic pulsations in the volume bounded by said surfaces and member.

9. A direct-acting diaphragm i or electro-acoustic apparatus, having a plurality of elements each rigid in itself, the edges of said elements being straight, two edges of each element being adjacent two edges of the other elements, and a flexible connection forming a straight-line hinge between the adjacent edges of such rigid elements, said elements forming a partial enclosure.

10. A direct-acting diaphragm for electroacoustic apparatus, having a plurality of substantially rectangular elements, said elements constituting the walls of a partial enclosure and a bridging member within the enclosure connecting the walls, and a flexible connection forming a straight-line hinge between straight adjacent edges of said rectangular elements.

11. A direct-acting diaphragm for electroacoustic apparatus having a plurality of elements 01' substantially rectangular form, a flexible connection between straight adjacent edges of said rectangular elements, and means for connecting other adjacent edges of said elements flexibly to stationary supports.

12. A direct-acting diaphragm for electroacoustic apparatus, having a plurality 01' substantially rectangular elements arranged with edges adjacent to form a. tubular enclosure and a central hinge connecting adjacent edges of said elements, two of the adjacent edges being connected to a stationary support.

13. A direct-acting diaphragm for electroacoustic apparatus, having a plurality of substantially rectangular elements, a central hinge connecting the adjacent edges of said elements, and means for connecting two adjacent edges of said elements to a stationary support.

14. A diaphragm for electro-acoustic apparatus, having a plurality of elements located side by side, a hinge connecting adjacent edges of said elements, and a metallic member embracing said hinge and clamped firmly thereon.

15. A sound reproducer comprising a hollow structure with yielding bowed walls, a bridging member within said structure joined to said walls so as to have a straight line hinge connection therewith, and means for imparting acoustic vibrations to said structure.

16. A sound reproducer comprising a tubular, hollow, open-ended structure with yielding oppositely bowed walls, a bridging member within said structure connecting said walls and joined thereto to form straight line hinges therewith, and means for producing relative movement between said walls and bridging member.

17. A sound reproducer comprising a hollow structure with yielding bowed walls, a bridging member having a central hinge portion and having hinge connection with said walls, and means for causing relative movement of said walls and member in response to sound wave impulses.

18. A sound reproducer comprising a hollow structure with yielding walls, a bridging member having a central hinge portion and having hinge connection with said walls, and means connected to the central hinge portion for causing relative movement of said walls and member in response to soimd wave impulses.

EDWDI H. SMYTHE. 

